The invention relates to an adhesive tape strip for a rereleasable adhesive bond which can be removed from a bonded joint by pulling in the direction of the bond plane.
Elastically or plastically highly extensible self-adhesive tapes which can be redetached nondestructively and without residue by stretching essentially in the bond plane (by what is known as stripping), even from in some cases highly sensitive bonding substrates, such as papers or coated wood-chip wallpaper, for example, are described in U.S. Pat. No. 4,024,312, DE 33 31 016, WO 92/11332, WO 92/11333, DE 42 22 849, WO 95/06691, DE 195 31 696, DE 196 26 870, DE 196 49 727, DE 196 49 728, DE 196 49 729 and DE 197 08 366. They are frequently employed in the form of adhesive tape strips having a preferably nonadhesive grip-tab region from which the detachment process is initiated. Particular applications and embodiments of such self-adhesive tapes can be found, inter alia, in DE 42 33 872, WO 94/21157, DE 44 28 587, DE 44 31 914, WO 97/07172, DE 196 49 636 and WO 98/03601.
Instances of tearing of such strippable self-adhesive tapes are a problem, especially in the region of the preferably nonadhesive grip tab and/or in the adhesive region directly bordering the preferably nonadhesive grip-tab region, and also in the main region of the bond, including the region between grip tab, or adhesive region close to the grip tab, and the end region of the adhesive strips. DE 44 31 914 describes a very specific measure for reducing the tendency to tear in the grip-tab region: surprisingly, it is found here that a significant reduction in the tendency to tear in the grip-tab region is obtained by using a cover in the grip-tab region, this cover having been made abhesive on the side facing the adhesive tape, and serving simultaneously as a grip tab for pulling. With this measure it is found, however, that the problems are not solved adequately and universally (i.e. for differently constructed products as well) and that it is necessary, moreover, to use abhesive, unwanted products.
DE 44 28 587 C2 also deals with the problem of tears in such adhesive tape strips, although in this case the tears occur at the end of the release process (cf. col. 1 lines 30-32), and as a countermeasure it proposes to give the ends of the adhesive tape strips a special shape in order for the bond area to decrease towards the end of the adhesive tape strip which disappears in the bonded joint whereas the other end can be pulled. Highly suitable examples given are pointed, zigzag and convexly curved strip ends, or else strips with a corrugated end boundary (cf. col. 1 lines 55-64). However, even adhesive tape strips of this kind continue to result in tears.
The object of the invention was to remedy this situation and, in particular, to provide adhesive tape strips of the type described with which no tears, or virtually no tears, occur on release from adhesive bonds performed with them and with which, furthermore, release is easier and more convenient than has been possible to date.
This object is achieved by an adhesive tape strip as characterized in more detail in the claims.
The key feature of the adhesive tape strip of the invention is that it is not, or not only, its end which disappears in the bonded joint that is specially shaped by means of the bond area decreasing towards the end in this region, but that the bond area in the front region of the adhesive tape strip (xe2x80x9cfrontxe2x80x9d because in the case of an adhesive bond it is this region which is located in the front part of the bonded joint, in contrast to the back region of the adhesive tape strip, which is addressed in DE 44 28 587), i.e. in the region of the grip tab, decreases towards that end of the strip which is opposite the said region. In other words, the adhesive tape strip is provided with a specially configured bond area in the grip-tab region (see e.g. FIGS. 5 to 7) and/or in the adhesive region directly bordering the grip-tab region (see e.g. FIGS. 1 to 8), in contrast to the end region of the adhesive tape strip, which is configured in accordance with DE 44 28 587.
The configuration of the invention leads not only to substantially fewer tears when the adhesive bond is released by stripping but also to a more pleasing stripping process, especially for users with little power in their hands and arms, such as women, children and the elderly. Thus, typically an adhesive strip detached by stretching in the bond plane is stripped very carefully, and hence slowly, from the bonded joint by the user in the first moments of the detachment process. If the width of the adhesive strip to be removed is constant, then the force to be applied during the subsequent detachment process remains approximately constant and the adhesive strip is removed from the bonded joint at an approximately uniform rate over the remaining length. If, however, the adhesive strip decreases in width, then the force required to remove the adhesive strip from the bonded joint becomes less. For the user, the result of the reducing stripping force and the rising stripping rate which is observed simultaneously in the course of practical use is the sensation of a very easy and pleasing removal of the adhesive strips from the bonded joint. It is in fact possible in this way to realize adhesive strips which by virtue of a sharp decrease in adhesive-strip width appear, as far as the user is concerned, to undergo stripping automatically.
One cause of the reduced tearing tendency of adhesive-strip sections which taper in the grip-tab region or on the adhesive region bordering the grip-tab region may be that in the region of an adhesive-strip taper, as a result of the reduction in the stripping force, there occurs in practice an acceleration of the stripping rate as a result of the steadily decreasing stripping force; this leads to a more uniform removal of the adhesive strips from the bonded joint and, for example, instances of sticking of the adhesive strips in the extended state, as may take place if the adhesive strips are removed slowly, do not occur. Another reason might be that the greater the adhesive-strip width of the adhesive-strip regions removed previously from the bonded joint places them under a reduced tension in the course of further stripping, and, consequently, in these regions the likelihood of tears is reduced, which brings about an overall reduction in the tendency to tear in the course of the detachment process.
Surprisingly, therefore, it is found that, with the measures specified above, simple geometric forms of an adhesive tape strip become possible, these forms allowing more convenient stripping and, moreover, a significant reduction in the tendency to tear. Such measures can be deployed for the grip-tab region in combination with those from DE 44 31 914 and/or DE 44 28 587, or else alone. Thus a marked reduction in the tearing tendency is achieved by integration of adhesive-tape regions in which the adhesive strip steadily tapers.
Adhesive tape strips of the invention can be of single- or multi-layer construction. Suitable in principle are single-layer adhesive tapes in accordance with DE 33 31 016 and DE 42 22 849 or multi-layer adhesive tapes consisting of one or more layers of adhesive and of one or more film- or foam-comprising layers in accordance with U.S. Pat. No. 4,024,312, DE 195 31 696, DE 196 26 870, DE 197 08 366, DE 196 49 727, DE 196 49 728, DE 196 49 729 or else those in accordance with WO 92/11332, WO 92/11333 and WO 95/06691.
Intermediate foam carriers may advantageously be part of adhesive tape strips of the invention when, inter alia, the intention is to use, for example, those having a relatively high flexural rigidity. In accordance with the invention it is possible to employ both single-sided and double-sided pressure-sensitive adhesive tape strips, preference being given to those which exhibit pressure-sensitive adhesion on both sides.
Adhesive tape strips of the invention are preferably below about 30 mm in width; typical adhesive strip lengths are between about 20 mm and 100 mm, preferably between about 25 mm and 75 mm and, with particular preference, between about 30 mm and 60 mm. In the end region, adhesive strips can optionally be shaped in accordance with DE 44 28 587; for example, they may run to a point. Adhesive tape strips have typical thicknesses of between about 300 xcexcm and about 2500 xcexcm, preferably between 400 xcexcm and 1500 xcexcm. Where the adhesive tape strips include one or more foam-comprising layers, typical thicknesses of adhesive film strips are from about 300 xcexcm to about 5000 xcexcmm, preferably from about 400 xcexcm to about 3000 xcexcm, and with particular preference, from about 500 xcexcm to about 2000 xcexcm.
Adhesive tape strips of the invention having a width which steadily reduces in one or more defined regions, and adhesive strips having a width which steadily reduces over the entire bonding region or over the entire length of the strip, have an adhesive film strip width mid-way along the strip of approximately 90% of the width of the strip at the transition between pressure-sensitive adhesive region and grip tab, preferably of approximately 75% of the width of the strip at the transition between pressure-sensitive adhesive region and grip tab.
Typical applications of adhesive film strips described above are the fixing of light to moderately heavy articles, such as pictures, calendars, posters, decorations, notices, postcards, self-adhesive mounting devices, such as self-adhesive hooks, self-adhesive picture holders, etc., in the home and office sector. In one specific embodiment, the nonadhesive grip-tab regions of such adhesive strips are produced by coloured printing or coating with coloured films, foils or papers. An advantage in this case is that, as a result of the coloured design of the grip-tab regions, the grip tabs themselves remain readily visible. A further advantage is the more attractive appearance of such adhesive strips, for children, for example. In a further specific embodiment, the adhesive strips are on average between about 2 mm and about 5 mm wide and between about 20 mm and 40 mm long in the bonding region, so making it possible to obtain adhesive strips which are particularly suitable for the adhesive bonding of very small and very light articles, such as are typically fixed to notice boards, for example.
Particular preference is given to adhesive film strip shapes which can be punched with very little loss in accordance with DE 196 41 094. Selected examples of such shapes are depicted in FIGS. 9, 10 and 11. The aforementioned examples should be understood as exemplary selections from a host of possible shapes.
Typical presentation forms include, punched adhesive tape strip sections covered on one side with a release laminate (typically release paper or release film) which are present with their second pressure-sensitive adhesive side, rather like pressure sensitive adhesive labels, on release paper roll stock or release film roll stock and can be removed, for example, from a carton pack having a slot and optionally a tear-off means, or else those which are present on release paper sheet stock or release film stock. A preferred pack form is that of a booklet which contains a plurality of sheets of release paper or release film which bear adhesive strips of the invention. Further possibilities include cartons or cans containing adhesive tape strips covered on both sides with a release paper or with a release film. The abovementioned descriptions should be understood as selected examples from a host of possible presentation forms.